A major objective of the proposed research is to assess the effects of conditions of illumination (e.g., stimulus intensity, duration, and wavelength; luminance contrast; adaptation level; interocular stimulus delay) on the visual latent period, as measured both psychophysically and electrophysiologically on the same observers. The psychophysical studies will include four classes of experimental conditions that produce characteristic monocular spatial illusions (the Hess and Frohlich phenomena) and binocular depth illusions (the Pulfrich and Mach-Dvorak phenomena). Each of these illusions yields a measure of the visual latent period, based on the assumption that the visual latent period is inversely related to the intensity of illumination. Additional latency data for comparable conditions of illumination will be obtained by direct measures of these same observers' simple reaction time. Discrepancies noted between the measured magnitude of the various latency responses will receive further experimental and theoretical analysis to help clarify the difference between monocular and binocular response latency and to further assess the role of the neuromuscular component of the total reaction-time response. Planned experiments on stereoscopic depth-discrimination thresholds for targets presented separately to each eye under various conditions of interocular stimulus delay should yield important information on the spatio-temporal integration processes involved in this uniquely binocular visual function. The electrophysiological studies will be extended to include new data on the latent period of the retinal response (electroretinogram, ERG) for comparison with those obtained both on visual evoked cortical potentials (VECP) and in the psychophysical experiments for these same observers tested under comparable conditions of illumination. The new experiments will continue to concentrate on the development of a very sensitive intra-subject index for early detection of unilateral pathology in the visual centers or pathways and for assessing the quality of binocular depth discrimination.